1. Field
A magnetic resonance imaging (MRI) system is concerned with diagnosing various diseases using a magnetic resonance image, and a susceptibility-weighted imaging (SWI) method.
2. Description of the Related Art
A medical imaging system acquires image information concerning a patient. Medical imaging systems include an X-ray apparatus, an ultrasonic diagnostic apparatus, a computed tomography (CT) apparatus and an MRI apparatus for example. An MRI apparatus provides a relatively flexible image capturing method, with improved contrast in soft tissue, provides various diagnostic information images, and is of value in diagnosis using medical images. A magnetic resonance image is acquired by imaging the density and chemicophysical property of atomic nuclei when nuclear magnetic resonance of hydrogen nuclei in the human body is caused using a magnetic field that is harmless to the human body and results in a radio frequency (RF) signal comprising non-ionizing radiation.
An MRI apparatus provides a predetermined frequency and energy to atomic nuclei within a predetermined magnetic field, thereby converting energy emitted from the nuclei into a signal used for imaging the inside of the human body. Protons within an atomic nucleus have individual spin angular momentums and magnetic dipoles. Thus, when a magnetic field is applied to the protons, the protons are arranged in the direction of the magnetic field, and the nucleus undergoes a precessional motion about the direction of the magnetic field.
Difference in magnetic susceptibility between pieces of body tissue are indicated by the degree of contrast between the pieces of body tissue associated with the longitudinal (or spin-lattice) relaxation time T1 decay constant, the transverse (or spin-spin) relaxation time T2 decay constant for a proton spin component or a proton density-weighted image. A method of acquiring an image in which difference in the degree of contrast between pieces of tissue is emphasized using such susceptibility difference is referred to as SWI (Susceptibility-Weighted Imaging). When susceptibility is weighted using a long time echo (TE), an artifact is included in a susceptibility-weighted image due to signal attenuation that may occur at an air cavity included in human body, for example, the nose or an ear.